Wednesday, 14 March 2012

Retro Wednesday 1: Zoning Laws revisited

On a suggestion from one of my long standing readers and member of the original 'Look to Windward' -study group back in '04, I'm going to revisit some old posts. He quit rightly pointed out that the number of readers has increased (somewhat) and that most of you don't have the time to go back trough the thousand plus posts I've published, to sort out the diamonds in the fluff. Thanks H!

Subject: Zoning Laws.
First posted 22 March 2009

I don't know how many of you participate in multi-class events, but this situation can only happen there. Two boats - with distinctive different hull lengths - approach a leeward mark to be left to port.

The zone in the RRS is defined as:
The area around a mark within a distance of three hull lengths of the boat nearer to it. A boat is in the zone  when any part of her hull is in the zone.
In the animation I've drawn two circles, the bigger one is representing the area within three hull lengths using the Grey boat and the dotted circle is the same area but using the Red (smaller) boat's length.

In position 1 Red is closest to the mark, so neither of the two boats has reached the zone.

In position 2 Grey gets an inside overlap, but neither has reached the zone, yet

Just before position 3 Grey's bow has passed the bow of Red and she is now the boat closest to the mark. The zone therefore is now represented by the bigger circle, which means that both boats are completely in the zone.

In position 4 Red bears away - sailing by the lee - and Grey sails to the mark and rounds it. As does Red.

Is Grey entitled to do this, in other words does Red have to give mark-room?
If possible. give me your analysis with the relevant rules

If you can't wait and want to peak to find the answer, read the comments after the original post: Zoning Laws


PS: Although the Poll has not yet run its total number of days, the predictions indicate a overwhelming majority of readers want the 'Full Monty' in their mail-box or feedreader. So as of yesterday I've changed the settings accordingly.


  1. I think yes, Red has to give mark room to Grey as just before position 3, when Grey's bow passes ahead of Red's, the zone is determined by Grey's hull lengths because she is nearer to the mark. The 2 boats are overlapped so the outside boat shall give the inside mark-room[RRS 18.2(a)]. But because Grey obtained an inside overlap from clear astern, if the outside boat, from the time the overlap began, was unable to give mark-room, she is not required to give it[RRS 18.2(e)].
    But how easy is for a PC to determine if just before position 3 Red is outside or not from the zone(her zone)?

    1. If Red reached (her) zone before Grey got clear ahead, rule 18.2(b) would dictate that Grey has mark-room.
      If not, it is like you state not rule 18.2(a) that does the same. In both cases Grey gets mark-room

  2. At moment Grey is closer to the mark than Red, rule 18 switches on – both boats are required to leave the mark on the same side and at least one of them (actually both of them) are in the zone (rule 18.1).

    I don’t believe rule 18.2(b) applies as neither boat “reaches” the zone – the zone instantaneously expands from being three of Red’s hull lengths to being three of Grey’s hull lengths.

    But 18.2(a) still applies – Red overlapped outside Grey is required to give her mark-room.

    And whilst Grey obtained inside overlap from clear astern, at the moment the overlap began Red (outside) was able to give Grey mark-room, and so 18.2(e) does not apply.


    1. There's on critical point where Grey is still only keep clear boat until her bow gets in front of Red. Until that moment she's not entitled to mark-room and must keep clear.
      After that moment Red must (be able) give mark-room.


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